1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to a method of fabricating a liquid crystal display device. Although the present invention is suitable for a wide scope of applications, it is particularly suitable for removing a hangover of an organic insulating layer around an edge portion of a pad by using a diffraction mask.
2. Discussion of the Related Art
A liquid crystal display device as a transmissive flat display device is widely applied to various electronic equipments, such as mobile phones, personal digital assistants (PDA's), and notebook computers. Recently, the LCD has been in the spotlight due to its advantages, such as light weight, slim shape, and high definition reproducibility. Furthermore, according to the increase in demand for a digital TV, a high definition TV, and a panel type TV, researches on a wide screen LCD have been actively proceeded.
Generally, an LCD is divided into several types according to the method of driving liquid crystal molecules. Recently, a thin film transistor-liquid crystal display (TFT-LCD) having a rapid response speed and less residual image is mainly used.
FIG. 1 is a plane view illustrating a structure of a TFT liquid crystal display device. As shown in FIG. 1, the TFT liquid crystal display device 1 includes a first substrate 3, a second substrate 5, and a liquid crystal layer 17 formed therebetween. On the first substrate 3, a plurality of gate lines 11 and data lines 13 defining a plurality of pixels are arranged in horizontal and vertical directions, each gate line 11 and each data line 13 is electrically connected to a driving device (not shown) through pads 12 and 14 formed in a non-display region of the first substrate 3. In addition, a TFT 15 is formed in each pixel. According to a scan signal applied through the gate line 11, the TFT 15 is switched, and an image signal inputted through the data line 13 is applied to the liquid crystal layer 17.
A sealing region having a sealant coated thereon is formed at the edge portion of the first and second substrates 3 and 5 in order to attach the first and second substrates 3 and 5 to each other. Herein, as shown in FIG. 1, a black matrix as a light shielding member is formed in the sealing region in order to prevent the light from transmitting the sealing region. The black matrix 9 is formed on the upper substrate 5, and only the sealing region is shown in FIG. 1. However, the black matrix 9 is formed between each pixel or on the TFT region and prevents the light transmittance as the non-display region of the liquid crystal display device.
In FIG. 1, the reference numeral 20 is a liquid crystal injection hole 20 for injecting liquid crystal after attaching the first and second substrates 3 and 5. After injecting the liquid crystal through the liquid crystal injection hole 20, it is encapsulated by an encapsulation material 22. Because the encapsulation material 22 is generally made of photo-sensitive materials, after filling the encapsulation material 22 in the liquid crystal injection hole 20, light, such as ultraviolet rays, is irradiated in order to harden the encapsulated material.
FIGS. 2A to 2G illustrate the method of fabricating a liquid crystal display device in accordance with the related art. Herein, the liquid crystal display device uses a passivation layer made of an organic material in order to protect the TFT. The liquid crystal display device is divided into a pixel region and an edge region for simplicity.
First, as shown in FIG. 2A, a metal such as Al or Al alloy or Cu is deposited on the first substrate 3, which is formed of a transparent material, such as glass, by an evaporating method or sputtering method. Etching is then performed with an etchant. A gate electrode 41 including a single layer or a plurality of layers is formed on the pixel region, a gate pad 12 is formed on the edge region, and a gate insulating layer 32 is deposited thereon. Also, a semiconductor material, such as amorphous silicon (a-Si), is deposited by a chemical vapor deposition (CVD) method, and etching is then performed. Accordingly, a semiconductor layer 42 is formed on the pixel region. A metal, such as Cr, Mo, Al, Al alloy or Cu, is deposited by the evaporating or sputtering method, and etching is then performed with an etchant. Thus, a source electrode 43 and a drain electrode 44 made of one or more layers are formed. Herein, as shown in FIG. 2A, a data line 105 is formed on a gate insulating layer 122, at the same time as the forming of the source electrode 16 and the drain electrode 117
Thereafter, a passivation layer 34 is formed by depositing an organic material, such as benzo cyclo butene (BCB) or photo-acryl, on the entire first substrate 3.
And, as shown in FIG. 2B, a photoresist layer 51 is formed by depositing a photoresist on the passivation layer 34, a diffraction mask 55 is arranged thereon, and light such as ultraviolet rays is irradiated. The diffraction mask 55 can transmit and shield the light. The intensity of the transmitted light may be adjusted by using a slit type diffraction mask having slits at set intervals. Accordingly, when the light is irradiated on the photoresist layer 51 by using the diffraction mask 55 and a developer is applied, as shown in FIG. 2C, the upper portion of the drain electrode 44 and the photoresist on the upper portion of the gate pad 12 are removed, and a part of the photoresist on the side portion of the gate pad 12 is removed. (A sealant is printed on the portion in order to attach the liquid crystal panel. Hereinafter, it is referred to as a sealing region.)
Afterwards, by etching the passivation layer 34 with the photoresist layer 51 remaining thereon, as shown in FIG. 2D, the upper portion of the drain electrode 44 in the pixel region and the passivation layer 34 on the upper portion of the gate pad 12 in the edge region are removed, and contact holes 36 and 37 are respectively formed at the upper portion of the drain electrode 44 in the pixel region and the upper portion of the gate pad 12 in the edge region.
And, after exposing the passivation layer 34 in the sealing region, by further developing the photoresist layer 51 on the passivation layer 34, the passivation layer 34 is etched, and accordingly a hole 38 is formed on the passivation layer 34 in the sealing region, as shown in FIG. 2E. Afterwards, by depositing a transparent electrode, such as indium tin oxide (ITO) or indium zinc oxide (IZO), on the passivation layer 34 in the pixel region and the edge region, a pixel electrode 47 contacting the drain electrode 44 through the contact hole 36 is formed at the pixel region, and a metal layer 48 is formed on the gate pad 12 in the edge region.
In the meantime, as shown in FIG. 2G, a black matrix 52 and a color filter layer 54 as formed on the second substrate 5 formed of a transparent material such as glass. A sealant 62 is printed onto the sealing region, and the first and second substrates 3 and 5 are attached by a pressure difference. Herein, because the sealant 62 has a poor adhesion characteristic with an organic material, the sealant 62 is contacted with the gate insulating layer 32 through the hole 38 formed at the sealing region, and accordingly the first and second substrates 3 and 5 are attached to each other.
As described above, in the related art method of fabricating the liquid crystal display device, the fabrication process is simplified by forming the contact hole on the gate pad 12 in the edge region or forming the hole 38 for the sealant adhesion.
However, in the use of the diffraction mask, problems that occur will be described as follows.
FIG. 3 is a plane view illustrating the edge region of the liquid crystal panel according to the related art. The diffraction mask 55 is arranged in order to expose the gate pad 12. As described in FIG. 3, the light is irradiated on the pad (namely, a photoresist formed on the pad) through a slit portion, at which a plurality of slits having the same width are formed, of the diffraction mask 55 arranged in the edge region.
FIGS. 4A and 4B are cross-sectional views illustrating the process for exposing the pad in the edge region by using the organic insulating layer according to the related art. First, as shown in FIG. 4A, by irradiating light through the diffraction mask 55 and applying the developer on the photoresist layer 51 formed on the upper portion of the organic insulating layer 34, the photoresist layer 51 is developed. And, as shown in FIG. 4B, by etching the passivation layer 34 formed of the organic material and etching the gate insulating layer 32 on the gate pad 12, the gate pad 12 is exposed to the outside, and the metal layer 48 made of ITO or IZO is formed on the gate pad 12.
In the meantime, the gate insulating layer 32 formed of an organic material has a height difference by the thickness of the gate pad 12. And, the uniform thickness of the passivation layer 34 is removed by etching along the entire substrate 3. More specifically, because the passivation layer 34 on the gate pad 12 and the passivation layer 12 between the gate pads 12 are uniformly removed, as shown in FIG. 4B, the passivation layer 34 as the organic material remains on the gate insulating layer 32 between the gate pads 12. When the metal layer 48 such as ITO or IZO is formed, the metal layer 48 is formed on the organic passivation layer 34. However, because interfacial characteristics between the metal layer 48 and the organic material are poor, the metal layer 48 is separated from the organic passivation layer 32 in forming of the metal layer 48, and accordingly deficiency occurs in the liquid crystal display device.